Adhesives and sealants based on telechelic polymers and heterotelechelic block polymers with dual cure systems

ABSTRACT

Pressure sensitive structural adhesive and sealant compositions comprising: (a) a polymer system comprising from 95 to 15 percent by weight of a telechelic polymer and from 5 to 85 percent by weight of a heterotelechelic polymer wherein at least one of the functionalities thereon is the same as the functionality on the telechelic polymer, and (b) a dual curing system wherein one element of the curing system cures the telechelic polymer and the common functionality on the heterotelechelic polymer and the other element cures the functionality on the heterotelechelic polymer but does not cure under the conditions required to cure the telechelic polymer to form a structural adhesive or sealant composition. In a preferred embodiment, the polymer system is comprised of a hydroxyl functional telechelic diol or polyol polymer and the heterotelechelic polymer is a monohydroxylated polydiene polymer which also has epoxidized olefin functionality. The dual curing system preferably is comprised of an isocyanate curing agent to cure through the hydroxyl groups at ambient temperatures to form a pressure sensitive adhesive or sealant and an amino resin to cure through the epoxy functionality upon baking to form a structural adhesive or sealant.

REFERENCE TO PRIOR APPLICATION

This is a division of application Ser. No. 08/519,885, filed Aug. 28,1995, now U.S. Pat. No. 5,576,388, which is a continuation-in-part ofSer. No. 08/320,808, filed Oct. 11, 1994, abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to pressure sensitive adhesivecompositions which can be further cured after being applied to asubstrate, making them behave as structural adhesives. Moreparticularly, the present invention provides adhesive and sealantcompositions based on a mixture of a telechelic polymer having hydroxylfunctionality with a heterotelechelic polymer having both hydroxyl andanother type of functionality and a dual curing system such as anisocyanate and a melamine.

Pressure sensitive adhesives based on block copolymers of conjugateddienes and/or vinyl aromatic hydrocarbons are well known. They have theparticular advantage that they give an instantaneous bond under lightpressure. The limitation of pressure sensitive adhesives is that theylack the cohesive strength to bear high loads. Structural andsemi-structural adhesives based on such polymers are also well known.Their advantage is that they cure to give adhesives which can bear quitehigh loads. Their disadvantage is that they must be applied as liquidsin order to achieve good bonding and so the assembly must be fixtureduntil the adhesives sets, usually by chemical cure, but sometimes bycooling from the melt.

It would be highly advantageous to provide a pressure sensitive adhesivewhich would give an instantaneous bond while having enough cohesivestrength that fixturing requirements would be less demanding orunnecessary and which would cure further upon some subsequent treatment,thereby increasing its cohesive strength so it becomes a structural orsemi-structural adhesive. The present invention provides such acomposition which is useful in both adhesives and sealants.

SUMMARY OF THE INVENTION

The present invention relates to pressure sensitive structural adhesiveand sealant compositions comprising a polymer system and a curing systemwherein the polymer system is comprised of from 95 to 15 percent byweight of a hydroxy functional telechelic polymer, from 5 to 85 percentby weight of a heterotelechelic polymer having at least one hydroxylgroup and at least one other functional group which does not reactsignificantly with the curing agent for the telechelic polymer, andwherein the curing system is comprised of a curing agent for thetelechelic polymer and a separate curing agent for the otherfunctionality on the heterotelechelic polymer which will not cure theheterotelechelic polymer under conditions used to cure the telechelicpolymer but will cure it under more severe conditions, i.e., highertemperature and/or pressure and/or exposure to radiation.

In a preferred embodiment, the polymer system is comprised of a hydroxylfunctional telechelic diol or polyol polymer and the heterotelechelicpolymer is a monohydroxylated polydiene polymer which also hasepoxidized olefin functionality. The dual curing system preferably iscomprised of an isocyanate curing agent to cure through the hydroxylgroups at ambient temperatures to form a pressure sensitive adhesive orsealant and an amino resin to cure through the epoxy functionality uponbaking to form a structural adhesive or sealant.

DETAILED DESCRIPTION OF THE INVENTION

The polymer system is comprised of both a telechelic polymer and aheterotelechelic polymer. A telechelic polymer is one which has aparticular type of functional group attached at the ends of themolecule. Telechelic polymers are typically diols, triols and starpolyols. Telechelic polymers can be made by the well known process ofring opening polymerization of cyclic monomers with an initiator,typically a polyfunctional alcohol. Examples are the ring openingpolymerization of monomers like ethylene oxide, propylene oxide,butylene oxide, or caprolactone, initiated by ethylene glycol to givediols or by glycerol to give triols. Another well known process to maketelechelic polymers is by anionic polymerization with a hydroxyfunctional initiator followed by reaction with a capping agent such asethylene oxide which, after termination, yields a hydroxyl group on theends of the polymer.

A heterotelechelic polymer is one which has one type of functional groupat or near one end of the molecule and another type of functional groupat or near the other end of the molecule. As will be seen from thefollowing discussion, the functionality may be throughout an end blockof a block copolymer and the block copolymer is a heterotelechelicpolymer within the scope of this invention. There must be differentfunctionalities and they must be separated, such as in the epoxidizedmonols described below, where an epoxidized end block of a diblockpolymer is separated from a terminal hydroxyl group by the entire lengthof the second block. Anionic polymerization is also a convenient way tomake heterotelechelic polymers. For example, polymers can be made whichhave ethylenic unsaturation in the molecule via polymerization of adiene monomer and also have a terminal functional group via a cappingreaction, for example a hydroxyl group via capping with ethylene oxide.The ethylenic unsaturation may be useful as is in the heterotelechelicpolymer or it can be used for further functionalization reactions, suchas epoxidation.

Anionic polymerizations are usually carried out in solution. Whenpolymerized to high molecular weight, the polymer will generally berecovered as a solid such as a crumb, a powder, a pellet or the like.When polymerized to low molecular weight, it may be recovered as aliquid such as in the present invention.

In general, when solution anionic techniques are used, copolymers ofconjugated diolefins, optionally with vinyl aromatic hydrocarbons, areprepared by contacting the monomer or monomers to be polymerizedsimultaneously or sequentially with an anionic polymerization initiatorsuch as group IA metals, their alkyls, amides, silanolates, napthalides,biphenyls or anthracenyl derivatives. It is preferred to use an organoalkali metal (such as sodium or potassium) compound in a suitablesolvent at a temperature within the range from about -150° C. to about300° C., preferably at a temperature within the range from about 0° C.to about 100° C. Particularly effective anionic polymerizationinitiators are organo lithium compounds having the general formula:

    RLi.sub.n

wherein R is an aliphatic, cycloaliphatic, aromatic or alkyl-substitutedaromatic hydrocarbon radical having from 1 to about 20 carbon atoms andn is an integer of 1 to 4.

Conjugated diolefins which may be polymerized anionically include thoseconjugated diolefins containing from about 4 to about 24 carbon atomssuch as 1,3-butadiene, isoprene, piperylene, methylpentadiene,phenyl-butadiene, 3,4-dimethyl-1,3-hexadiene, 4,5-diethyl-1,3-octadieneand the like. Isoprene and butadiene are the preferred conjugated dienemonomers for use in the present invention because of their low cost andready availability. Alkenyl (vinyl) aromatic hydrocarbons which may becopolymerized include vinyl aryl compounds such as styrene, variousalkyl-substituted styrenes, alkoxy-substituted styrenes, vinylnapthalene, alkyl-substituted vinyl napthalenes and the like.

The hydroxyl groups of both the telechelic and heterotelechelic polymersof the present invention will react with the isocyanate curing agent atambient conditions to form a pressure sensitive adhesive or sealantcomposition while the other type of functionality will only cure uponbaking at a temperature of at least 100° C. to make a structuraladhesive or sealant composition.

The telechelic polymer provides the strength to the ambient curedpressure sensitive adhesive or sealant composition. If the telechelicpolymer is a diol or polyol, there are many types which can be used.Polydiene diols and polyols (radial), as well as their saturatedanalogs, can be used, as well as polyether, polyester, and acrylic diolsand polyols (radial). The preferred telechelic polymers for use in thepresent invention are diols and polyols of conjugated dienes, preferablyhydrogenated diols and polyols of conjugated dienes.

There are many types of heterotelechelic polymers which can be usedherein. As stated above, one end of the heterotelechelic polymer willhave the same functional group as the telechelic polymer. The other endwill have a different type of functional group which does not react withits crosslinker under the same conditions used to crosslink thetelechelic polymer. Heterotelechelic polymers may include those whereinprotected functional initiators and/or protected functional cappingagents are included into the polymer. Heterotelechelic polymers can alsobe made by functionalization reactions on telechelic polymers.

In the preferred embodiment of this invention the polymer system is acombination of hydroxy functional telechelic and heterotelechelicpolymers wherein the other functionality on the heterotelechelic polymeris an olefinic epoxy. The curing system is an isocyanate for ambientcure and a melamine resin for bake cure after the adhesive has beenapplied. However, this invention is not restricted to these chemistries.The following are some examples of other suitable telechelic andheterotelechelic polymers. If the telechelic polymer has hydroxylfunctionality, the heterotelechelic polymer will also have a hydroxylgroup and also another type of functional group such as C═C unsaturation(for sulfur cure or melamine cure), acrylic unsaturation (for freeradical cure via peroxide or radiation), epoxidized olefin (for cationiccure via a blocked Lewis acid or for radiation cure or for melaminecure), or glycidyl ether epoxy (for acid or anhydride cure or catalyticcure). If the telechelic polymer has acrylic unsaturation (for freeradical cure at ambient temperature via peroxide or radiation), theheterotelechelic polymer will also have an acrylic group and anotherfunctional group such as hydroxy functionality (for melamine or blockedisocyanate cure), olefinic unsaturation, glycidyl ether epoxy, orepoxidized olefin functionality. If the telechelic polymer has glycidylether functionality (for ambient cure with aliphatic amines), theheterotelechelic polymer will have glycidyl ether epoxy functionalityand another functional group such as olefinic unsaturation, epoxidizedolefin, or hydroxy functionality. There are many other combinations forfunctional groups and curing systems and thus there are manypossibilities for dual curing systems.

The telechelic polydiene polymers are preferably synthesized by anionicpolymerization of conjugated diene hydrocarbon monomers, such asbutadiene or isoprene with lithium initiators. The process steps areknown as described in U.S. Pat. Nos. 4,039,593, Re. 27,145, and U.S.Pat. No. 5,376,745 which descriptions are incorporated herein byreference. Polymerization begins when a dilithium or polylithiuminitiator builds a living polymer backbone at each lithium site. Typicaldilithium living polymer structures containing conjugated dienehydrocarbons are:

Li--B--X--B--Li

Li--B--A--X--A--B--Li

Li--A--B--A--X--A--B--A--Li

wherein B represents polymerized units of one or more conjugated dienehydrocarbons such as butadiene or isoprene, A represents polymerizedunits of one or more conjugated dienes and/or vinyl aromatic compoundssuch as styrene, and X is the residue of the diinitiator, such as theinitiator formed by reaction of diisopropenyl benzene with two moles ofsec-butyllithium. B can also be a copolymer of a conjugated diene and avinyl aromatic compound.

The anionic polymerization is done in solution in an organic solvent,typically a hydrocarbon like hexane, cyclohexane or benzene, althoughpolar solvents such as tetrahydrofuran can also be used. When theconjugated diene is 1,3-butadiene and when the resulting polymer will behydrogenated, the anionic polymerization of butadiene in a hydrocarbonsolvent like cyclohexane is typically controlled with structuremodifiers such as diethylether or glyme (1,2-diethoxyethane) to obtainthe desired amount of 1,4-addition. As described in U.S. Pat. No. Re27,145 which is incorporated by reference herein, the level of1,2-addition of butadiene in the polymer or copolymer can greatly affectviscosity and elastomeric properties after hydrogenation.

The optimum balance between low viscosity and high solubility in ahydrogenated polybutadiene polymer occurs at about a 60/40 ratio of1,4-butadiene/1,2-butadiene. This butadiene microstructure is achievedduring polymerization at 50° C. in cyclohexane containing about 6% byvolume of diethylether or about 1000 ppm of glyme. This is not a concernwhen isoprene is the monomer used to make the hydrogenated polydienepolymer and so the polymerization can be done in a pure hydrocarbonsolvent with no modifier. The hydrogenated polymers exhibit improvedheat stability and weatherability in the final adhesive or sealant.

After polymerization of the monomers is complete, the hydroxyl groupsare added by capping the living polymer chain ends with a capping agent,typically ethylene oxide, and terminating with a proton donor, typicallymethanol.

A saturated, dihydroxy polydiene polymer can also be made using amono-lithium initiator which contains a hydroxyl group which has beenblocked as the silyl ether. Details of the polymerization procedure canbe found in U.S. Pat. No. 5,376,745, which is herein incorporated byreference. A suitable initiator is hydroxypropyllithium in which thehydroxyl group is blocked as the tert-butyl-dimethylsilyl ether. Thismono-lithium initiator can be used to polymerize isoprene or butadiene,with or without styrene, in hydrocarbon or polar solvent. The molarratio of initiator to monomer determines the molecular weight of thepolymer. The living polymer is then capped with one mole of ethyleneoxide and terminated with one mole of methanol to yield the mono-hydroxypolydiene polymer. The silyl ether is then removed by acid catalyzedcleavage in the presence of water yielding the desired dihydroxypolydiene polymer.

Polyhydroxylated polydiene polymers can be obtained using similartechnology. Mulitfunctional-lithium initiators can be prepared fromreaction of sec-butyllithium with diisopropenylbenzene at less than a2:1 molar ratio. These multi-lithium initiators can then be used topolymerize butadiene in solvent. The living polymers would then becapped with ethylene oxide and terminated with methanol to give thepolyhydroxylated polydiene polymer. Alternatively, the protectedmono-lithium initiator can be used to polymerize butadiene or isoprene.The living polymer can be coupled with a multifunctional coupling agentand the blocking agent would then be removed, regenerating the hydroxylgroup. A trifunctional coupling agent like methyltrimethoxysilane wouldyield a tri-hydroxy polydiene polymer. A tetrafunctional coupling agentlike silicon tetrachloride would yield a tetra-hydroxy polydienepolymer. A propagating coupling agent like divinylbenzene would yield amulti-hydroxy polydiene polymer having up to 20 hydroxyl groups perpolydiene polymer.

The heterotelechelic monohydroxylated polydiene polymers are alsosynthesized by anionic polymerization of conjugated diene hydrocarbons,such as butadiene or isoprene, with lithium initiators. The processsteps are the same as for the multifunctional telechelic polymers exceptpolymerization commences with a monolithium initiator instead of themultilithium initiator.

The hydroxylated polydiene polymers of this invention will have hydroxylequivalent weights between about 500 and about 20,000, preferablybetween 1000 and 15,000, and most preferably between 2000 and 10,000.Thus, for monohydroxy polydiene polymers, suitable peak molecularweights will be between 500 and 20,000. Below the lower molecular weightrange, cost becomes prohibitively high because of the high cost of thepolymerization initiator. Above the higher molecular weight range,viscosity becomes somewhat high making mixing and application of theadhesive more difficult and, at such high hydroxyl equivalent weights,it becomes difficult to accomplish the required polyurethane chemistry.Preferably, the telechelic polymer is a diol or polyol of at least oneconjugated diene such as polybutadiene diol or polyisoprene diol or itmay have the formula

    HO--A--S.sub.z --B--OH

or

    (HO--A--S.sub.z --B).sub.n --Y

wherein A and B are polymer blocks which may be homopolymer blocks ofconjugated diolefin monomers, copolymer blocks of conjugated diolefinmonomers, or copolymer blocks of diolefin monomers and monoalkenylaromatic hydrocarbon monomers, S is a vinyl aromatic hydrocarbon block,Y is a coupling agent, z is 0 or 1, and n is an integer from 1 to 20.

The heterotelechelic polymer preferably is an epoxidizedmonohydroxylated polydiene polymer which is comprised of at least twopolymerizable ethenically unsaturated monomers wherein at least one is adiene monomer that yields unsaturation suitable for epoxidation. Thehydroxylated heterotelechelic polymers are most preferably blockcopolymers of at least two conjugated dienes, preferably isoprene andbutadiene, and, optionally, a vinyl aromatic hydrocarbon wherein ahydroxyl group is attached at one end of the polymer molecule. Thesepolymers may be hydrogenated or unhydrogenated.

The preferred epoxidized monohydroxylated polydiene polymer of thepresent invention is described in detail in copending, commonlyassigned, U.S. patent application Ser. No. 08/320,805 entitled,"Monohydroxylated Diene Polymers and Epoxidized Derivatives Thereof",filed concurrently with the parent application of this application andwhich is herein incorporated by reference, and has the structuralformula

    A--S.sub.z --B--OH                                         (I)

wherein A and B are polymer blocks which may be homopolymer blocks ofconjugated diolefin monomers, copolymer blocks of conjugated diolefinmonomers, or copolymer blocks of diolefin monomers and monoalkenylaromatic hydrocarbon monomers. These polymers may contain up to 60% byweight of at least one vinyl aromatic hydrocarbon, preferably styrene.The A blocks have a greater concentration of more highly substitutedaliphatic double bonds than the B blocks have. Thus, the A blocks have agreater concentration of di-, tri-, or tetra-substituted unsaturationsites (aliphatic double bonds) per unit of block mass than do the Bblocks. This produces a polymer wherein the most facile epoxidationoccurs in the A blocks and thus, when these polymers are epoxidized, aheterotelechelic polymer is formed with the hydroxyl on one end and theepoxy groups in the other end block. The A blocks have a molecularweight of from 100 to 6000, preferably 500 to 4,000, and most preferably1000 to 3000, and the B blocks have a molecular weight of from 1000 to15,000, preferably 2000 to 10,000, and most preferably 3000 to 6000. Sis a vinyl aromatic hydrocarbon block which may have a molecular weightof from 100 to 10,000. z is 0 or 1. Either the A or the B block may becapped with a miniblock of polymer, 50 to 1000 molecular weight, of adifferent composition, to compensate for any initiation, tapering due tounfavorable copolymerization rates, or capping difficulties. Thesepolymers are epoxidized such that they contain from 0.2 to 7.0milliequivalents (meq) of epoxy per gram of polymer.

The most highly preferred polymers for use herein are diblock polymerswhich fall within the scope of formula (I) above. The overall molecularweight of such diblocks may range from 1500 to 15000, preferably 3000 to7000. Either of the blocks in the diblock may contain some randomlypolymerized vinyl aromatic hydrocarbon as described above. For example,where I represents isoprene, B represents butadiene, S representsstyrene, and a slash (/) represents a random copolymer block, thediblocks may have the following structures:

I--B--OH I--B/S--OH I/S--B--OH or

B/I--B/S--OH I--EB--OH I--EB/S--OH or

I--S/EB--OH I/S--EB--OH

where EB is hydrogenated butadiene, --EB/S--OH means that the hydroxylsource is attached to a styrene mer, and --S/EB--OH signifies that thehydroxyl source is attached to a hydrogenated butadiene mer. This lattercase, --S/EB--OH, requires capping of the S/EB "random copolymer" blockwith a mini EB block to compensate for the tapering tendency of thestyrene prior to capping with ethylene oxide. These diblocks areadvantageous in that they exhibit lower viscosity and are easier tomanufacture than the corresponding triblock polymers. The hydroxyl isattached to the butadiene block because the epoxidation proceeds morefavorably with isoprene and there will be a separation between thefunctionalities on the polymer. The isoprene blocks may also behydrogenated.

Certain triblock copolymers are also preferred for use herein. Suchtriblocks usually include a styrene block or randomly copolymerizedstyrene to increase the polymers glass transition temperature,compatibility with polar materials, strength, and room temperatureviscosity. These triblocks include the following specific structures:

I--EB/S--EB--OH I--B/S--B--OH I--S--EB--OH I--S--B--OH or

I--B--S--OH I--EB--S--OH

The latter group of polymers specified in the last line above whereinthe styrene block is external are represented by the formula

    A--B--S--OH                                                (II)

where A, B, and S are as described above.

The heterotelechelic hydroxylated polydienes synthesized by anionicpolymerization will also have olefinic unsaturation. Although thesepolymers may be useful as is, the olefinic unsaturation can also beepoxidized. Epoxidation of the base polymer can be effected by reactionwith organic peracids which can be preformed or formed in situ. Suitablepreformed peracids include peracetic and perbenzoic acids. In situformation may be accomplished by using hydrogen peroxide and a lowmolecular weight fatty acid such as formic acid. Alternatively, hydrogenperoxide in the presence of acetic acid or acetic anhydride and acationic exchange resin will form a peracid. The cationic exchange resincan optionally be replaced by a strong acid such as sulfuric acid orp-toluenesulfonic acid. The epoxidation reaction can be conducteddirectly in the polymerization cement (polymer solution in which thepolymer was polymerized) or, alternatively, the polymer can beredissolved in an inert solvent. These methods are described in moredetail in U.S. Pat. Nos. 5,229,464 and 5,247,026 which are hereinincorporated by reference.

The molecular weights of linear polymers or unassembled linear segmentsof polymers such as mono-, di-, triblock, etc., arms of star polymersbefore coupling are conveniently measured by Gel PermeationChromatography (GPC), where the GPC system has been appropriatelycalibrated. For anionically polymerized linear polymers, the polymer isessentially monodisperse (weight average molecular weight/number averagemolecular weight ratio approaches unity), and it is both convenient andadequately descriptive to report the "peak" molecular weight of thenarrow molecular weight distribution observed. Usually, the peak valueis between the number and the weight average. The peak molecular weightis the molecular weight of the main species shown on the chromatograph.For polydisperse polymers the weight average molecular weight should becalculated from the chromatograph and used. For materials to be used inthe columns of the GPC, styrene-divinyl benzene gels or silica gels arecommonly used and are excellent materials. Tetrahydrofuran is anexcellent solvent for polymers of the type described herein. Arefractive index detector may be used.

Measurement of the true molecular weight of a coupled star polymer isnot as straightforward or as easy to make using GPC. This is because thestar shaped molecules do not separate and elute through the packed GPCcolumns in the same manner as do the linear polymers used for thecalibration. Hence, the time of arrival at an ultraviolet or refractiveindex detector is not a good indicator of the molecular weight. A goodmethod to use for a star polymer is to measure the weight averagemolecular weight by light scattering techniques. The sample is dissolvedin a suitable solvent at a concentration less than 1.0 gram of sampleper 100 milliliters of solvent and filtered using a syringe and porousmembrane filters of less than 0.5 microns pore size directly into thelight scattering cell. The light scattering measurements are performedas a function of scattering angle, polymer concentration and polymersize using standard procedures. The differential refractive index (DRI)of the sample is measured at the same wave length and in the samesolvent used for the light scattering. The following references areherein incorporated by reference:

1. Modern Size-Exclusion Liquid Chromatography, M. W. Yau, J. J.Kirkland, D. D. Bly, John Wiley and Sons, New York, N.Y., 1979.

2. Light Scattering From Polymer Solutions, M. B. Huglin, ed., AcademicPress, New York, N.Y., 1972.

3. W. K. Kai and A. J. Havlik, Applied Optics, 12, 541 (1973).

4. M. L. McConnell, American Laboratory, 63, May, 1978.

If desired, these block copolymers can be partially hydrogenated.Hydrogenation may be effected selectively as disclosed in U.S. Pat. No.Reissue 27,145 which is herein incorporated by reference. Thehydrogenation of these polymers and copolymers may be carried out by avariety of well established processes including hydrogenation in thepresence of such catalysts as Raney Nickel, nobel metals such asplatinum and the like, soluble transition metal catalysts and titaniumcatalysts as in U.S. Pat. No. 5,039,755 which is also incorporated byreference. A particularly preferred catalyst is a mixture of nickel2-ethylhexanoate and triethylaluminum. The polymers may have differentdiene blocks and these diene blocks may be selectively hydrogenated asdescribed in U.S. Pat. No. 5,229,464 which is also herein incorporatedby reference. The telechelic polydiene polymers of this invention arepreferably hydrogenated such that at least 90%, preferably at least 95%,of the carbon to carbon double bonds become saturated. It is preferredthat the heterotelechelic polydiene polymers be partially unsaturated inorder that the carbon to carbon double bonds can be used as is or can beused for further functionalization such as to make the epoxidizedpolymers of this invention. The level of unsaturation in theheterotelechelic polymers should be from 0.2 to 7.5 meq of double bondsper gram of polymer.

The amount of the telechelic polymer used in the polymer part of theadhesive or sealant composition may range from 95 to 15% by weight. Ifless than 15% is used, the pressure sensitive adhesive will not havesufficient strength and if more than 95% is used, there will be toolittle of the heterotelechelic polymer to cure and increase cohesivestrength. The amount of the dual curing system will depend on the typeof functionality in the heterotelechelic polymer and on the particularcuring system used. Normally, however, the hydroxyl functionaltelechelic and heterotelechelic polymers will be cured with astoichiometric amount of isocyanate. If olefinic unsaturation is theother functionality in the heterotelechelic polymer, then a sulfur-basedcrosslinking system will be used at from 0.5 to 6% by weight. Ifepoxidized olefin is the other functionality in the heterotelechelicpolymer, then an amino resin crosslinker will be used at from 2 to 20%by weight.

The polyisocyanate used in this invention can be an aliphatic or anaromatic polyisocyanate or a mixture of the two. Aliphaticpolyisocyanates are generally preferred since they will give sealantsand adhesives having lighter color and better durability than aromaticpolyisocyanates. Since the telechelic and heterotelechelic saturatedhydroxylated polydiene polymers can have functionalities of as little as1 or 2 hydroxyl groups per molecule, it is necessary that the isocyanatehave a functionality of greater than 2 in order to assure that thepolyurethane sealant or adhesive composition will crosslink into acohesive mass. Typically, the polyisocyanate will have a functionalityof 3 or more isocyanate (NCO) functional groups per molecule. However,it is possible to use difunctional or monofunctional isocyanates incombination with polyfunctional isocyanates. The dual curing systempreferably contains an isocyanate having a equivalent weight between 50and 500.

Examples of suitable aromatic polyfunctional isocyanates are1,2,4-benzene triisocyanate, polymethylene polyphenyl isocyanate(Mondur® MR ex Bayer), the adduct of toluene diisocyanate withtrimethylolpropane (Mondur® CB-60 ex Bayer). Examples of suitablealiphatic polyfunctional isocyanates are the isocyanurate of isophoronediisocyanate (Desmodur® Z-4370 ex Bayer) and the isocyanurate of hexanediisocyanate (Desmodur® N-3390 ex Bayer). Desmodur® Z-4370 has beenfound to be a particularly effective triisocyanate for this inventionbecause it has excellent compatibility with the saturated, hydroxylatedpolydiene polymers of this invention. It gives clear, colorless sealantsand adhesives with excellent tack and peel and should also giveexcellent durability, even under exposure to sunlight.

Although isocyanates having 3 or more NCO groups per molecule will bethe major component of the polyisocyanate curing agent, small amounts ofdiisocyanates and monoisocyanates can also be used. Suitablediisocyanates are toluene diisocyanate, diphenyl methane diisocyanate,isophorone diisocyanate, dicyclohexyl methane diisocyanate and hexanediisocyanate. Suitable monoisocyanates are toluene isocyanate, phenylisocyanate and cyclohexyl isocyanate.

Polyisocyanate adducts can also be used in this invention. These aretypically made by capping a polypropylene oxide diol or triol or apolycaprolactone diol or triol with a diisocyanate.

When the heterotelechelic polymer has olefinic epoxy functionality, thecrosslinking agents which are useful in the present invention are aminoresins. For the purposes of this invention, an amino resin is a resinmade by reaction of a material bearing NH groups with a carbonylcompound and an alcohol. The NH bearing material is commonly urea,melamine, benzoguanamine, glycoluril, cyclic ureas, thioureas,guanidines, urethanes, cyanamides, etc. The most common carbonylcomponent is formaldehyde and other carbonyl compounds include higheraldehydes and ketones. The most commonly used alcohols are methanol,ethanol, and butanol. Other alcohols include propanol, hexanol, etc.American Cyanamid (renamed CYTEC) sells a variety of these amino resins,as do other manufacturers. American Cyanamid's literature describesthree classes or "types" of amino resins that they offer for sale.##STR1## where Y is the material that bore the NH groups, the carbonylsource was formaldehyde and R is the alkyl group from the alcohol usedfor alkylation. Although this type of description depicts the aminoresins as monomeric material of only one pure type, the commercialresins exist as mixtures of monomers, dimers, trimers, etc. and anygiven resin may have some character of the other types. Dimers, trimers,etc. also contain methylene or ether bridges. Generally, type 1 aminoresins are preferred in the present invention.

The amino resin must be compatible with both the telechelic and theheterotelechelic polymer. A compatible amino resin is defined as onewhich gives a phase stable blend with the polymers at the desiredconcentration and at the temperature at which the compositions will bemixed and applied. The dual curing system preferably contains an aminoresin having an equivalent weight between 50 and 500.

For example, the following type 1 amino resins can be used to achievethe purpose of the present invention: CYMEL® 1156--amelamine-formaldehyde resin where R is C₄ H₉, CYMEL® 1170--aglycoluril-formaldehyde resin where R is C₄ H₉, CYMEL® 1141--a carboxylmodified amino resin where R is a mixture of CH₃ and i-C₄ H₉, andBEETLE® 80--a urea-formaldehyde resin where R is C₄ H₉. All of theseproducts are made by American Cyanamid Company and are described in itspublication 50 Years of Amino Coating Resins, edited and written byAlbert J. Kirsch, published in 1986 along with other amino resins usefulin the present invention.

CYMEL® 1170 is the following glycoluril-formaldehyde resin where R is C₄H₉ : ##STR2## BEETLE®® 80 is a urea-formaldehyde resin where R is C₄ H₉whose ideal monomeric structure is depicted: ##STR3##

The adhesive and sealant compositions of this invention may consist onlyof the telechelic and heterotelechelic polymers along with the dualcuring system crosslinkers. However, it may be necessary for aformulator to combine a variety of ingredients together with thepolymers of the present invention in order to obtain products having theproper combination of properties (such as adhesion, cohesion,durability, low cost, etc.) for particular applications. Although asuitable formulation might contain only the polymers and curing agents,in most adhesive and sealant applications, suitable formulations wouldalso contain various combinations of resins, plasticizers, fillers,solvents, stabilizers and other ingredients such as asphalt. Thefollowing are some typical examples of formulating ingredients foradhesives and sealants.

In order to obtain high pressure sensitive adhesive tack, it may benecessary to add an adhesion promoting or tackifying resin that iscompatible with the polymers. A common tackifying resin is adiene-olefin copolymer of piperylene and 2-methyl-2-butene having asoftening point of about 95° C. This resin is available commerciallyunder the tradename Wingtack® 95 and is prepared by the cationicpolymerization of 60% piperlene, 10% isoprene, 5% cyclo-pentadiene, 15%2-methyl-2-butene and about 10% dimer, as taught in U.S. Pat. No.3,577,398. Other tackifying resins may be employed wherein the resinouscopolymer comprises 20-80 weight percent of piperylene and 80-20 weightpercent of 2-methyl-2-butene. The resins normally have ring and ballsoftening points as determined by ASTM method E28 between about 80° C.and 115° C.

Aromatic resins may also be employed as tackifying agents, provided thatthey are compatible with the particular polymers used in theformulation. Normally, these resins should also have ring and ballsoftening points between about 80° C. and 115° C. although mixtures ofaromatic resins having high and low softening points may also be used.Useful resins include coumarone-indene resins, polystyrene resins, vinyltoluene-alpha methylstyrene copolymers and polyindene resins.

Other adhesion promoting resins which are also useful in thecompositions of this invention include hydrogenated rosins, esters ofrosins, polyterpenes, terpenephenol resins and polymerized mixedolefins, lower softening point resins and liquid resins. An example of aliquid resin is Adtac® LV resin from Hercules. To obtain goodthermo-oxidative and color stability, it is preferred that thetackifying resin be a saturated resin, e.g., a hydrogenateddicyclopentadiene resin such as Escorez® 5000 series resin made by Exxonor a hydrogenated polystyrene or polyalphamethylstyrene resin such asRegalrez® resin made by Hercules. The amount of adhesion promoting resinemployed varies from 0 to 400 parts by weight per hundred parts polymer(php), preferably between 20 to 350 php, most preferably 20 to 150 php.The selection of the particular tackifying agent is, in large part,dependent upon the specific polymers employed in the adhesivecomposition.

A composition of the instant invention may contain plasticizers, such asrubber extending plasticizers, or compounding oils or organic orinorganic pigments and dyes. Rubber compounding oils are well-known inthe art and include both high saturates content oils and high aromaticscontent oils. Preferred plasticizers are highly saturated oils, e.g.Tufflo® 6056 and 6204 oil made by Arco and process oils, e.g. Shellflex®371 oil made by Shell. The amounts of rubber compounding oil employed inthe invention composition can vary from 0 to about 500 php, preferablybetween about 0 to about 100 php, and most preferably between about 0and about 60 php.

Various types of fillers and pigments can be included in theformulation. This is especially true for exterior adhesives or sealantsin which fillers are added not only to create the desired appeal butalso to improve the performance of the adhesives or sealants such astheir weatherability. A wide variety of fillers can be used. Suitablefillers include calcium carbonate, clays, talcs, silica, zinc oxide,titanium dioxide and the like. The amount of filler usually is in therange of 0 to about 800 php depending on the type of filler used and theapplication for which the adhesive or sealant is intended. An especiallypreferred filler is titanium dioxide.

Stabilizers known in the art may also be incorporated into thecomposition. These may be for protection during the life of the articleagainst, for example, oxygen, ozone and ultra-violet radiation or forprotection against degradation during mixing, application or curing.Typical stabilizers are antioxidants, usually hindered phenoliccompounds, and UV inhibitors, usually benzophenone or benzotriazolecompounds or hindered amine light stabilizers. The amount of stabilizerused depends highly on the application for which the composition isintended but generally, the stabilizers will be used at from 0.1 to 10php.

Most adhesive and sealant compositions based on this invention willcontain some combination of the various formulating ingredientsdisclosed herein. No definite rules can be offered about whichingredients will be used. The skilled formulator will choose particulartypes of ingredients and adjust their concentrations to give exactly thecombination of properties needed in the composition for any specificadhesive or sealant application. So, beyond the telechelic polymer, theheterotelechelic polymer and the two curing agent systems, theformulator will choose to use or not to use among the various resins,fillers and pigments, plasticizers, oligomers, stabilizers and solvents.

The key to the concept of the present invention is to make a pressuresensitive adhesive or sealant which can be further cured after it isapplied, making it behave as a structural adhesive or sealant. Theadhesive or sealant is based on a mixture of a telechelic polymer, suchas the preferred hydrogenated polydiene diol, with a heterotelechelicpolymer, such as the preferred epoxidized monohydroxylated polydienepolymer, and a dual curing system including, for example, an isocyanateand an amino resin. A pressure sensitive adhesive composition (orpressure sensitive sealant composition) is formed which can be appliedto a substrate. Later, when the assembly is baked, the composition curesthrough amino resin curing of the epoxy groups, further increasing thecohesive strength and modulus of the adhesive or sealant composition andmaking it perform more like a structural adhesive than a pressuresensitive adhesive. A specific use for such compositions is to make afree film which is a pressure sensitive adhesive between two layers ofrelease paper. This free film is then used to adhere automobile partstogether, such as hood and door reinforcements, with enough strength tohold them in place until the body is baked. Upon baking, the adhesivecures further, giving a structural or at least semi-structural bondholding the parts permanently in place. This use has the additionalbenefit that the free film of pressure sensitive adhesive between twolayers of release paper can be die cut to exactly the size and shapeneeded for the particular application.

EXAMPLES

In the following examples, the telechelic polymer (Polymer A) is a 3500molecular weight (MW) hydrogenated polybutadiene diol (HO--EB--OH).Three heterotelechelic polymers were used. All three were 6000 molecularweight. Polymer C is a 2000 MW polyisoprene block-2500 MWpolystyrene/1500 MW polybutadiene random copolymer block --OH(I--S/EB--OH) in which the polybutadiene has been selectivelyhydrogenated and the polyisoprene has been epoxidized to a level of 1.5meq epoxy/gm. Polymer D is a 2000 MW polyisoprene block-4000 MWpolybutadiene block --OH (I--EB--OH) in which the polybutadiene has beenselectively hydrogenated and the polyisoprene has been epoxidized to 1.5meq/gm. Polymer E is the same as Polymer D except the polyisoprene hasnot been epoxidized, but retains 1.5 meq/gm of double bonds. Polymer Bis a non-heterotelechelic polymer used for comparison with theheterotelechelic polymers. It is a 3000 MW hydrogenated polybutadienemonol (EB--OH). The HO--EB--OH was used with each of the four monols,with and without tackifying resin, by curing them through their hydroxylgroups with a trifunctional isocyanate, Desmodur® Z-4370, to give apolyurethane pressure sensitive adhesive (PSA) which also contained themelamine resin, CYMEL® 1156. The intent was that this PSA could be usedas any normal PSA to adhere two substrates together, giving aninstantaneous bond under light pressure and having sufficient shearstrength to hold the pieces together under modest load. Then, after theadhesive was in place, the assembly could be heated to accomplish themelamine cure through the epoxy groups and improve the shear strengthenough that the adhesive could bear high enough load that it couldperform as a structural adhesive.

To test this approach, formulations 1-4 in the table were prepared,using a 35/65 diol/monol ratio by weight. To 80 parts by weight (pbw) ofthis diol/monol mixture was added 18 pbw of the butylated melamineresin, CYMEL® 1156, and 2 pbw of dodecyl benzene sulfonic acid catalyst,CYCAT® 600 (CYCAT® 600 is a 70% w solution of acid in isopropylalcohol), to catalyze the melamine/epoxy reaction when the adhesive isbaked. This mixture was dissolved at 64% w solids in dry xylene to givethe hydroxyl side of the two-component polyurethane. Immediately beforecasting films of the adhesives, Desmodur® Z-4370 was added at astoichiometric 1/1 NCO/OH ratio (including the alcohol introduced withthe CYCAT® 600), along with 0.04% w dibutyl tin dilaurate catalyst(DABCO T-12), to catalyze the isocyanate/hydroxyl reaction. Theseadhesive solutions were cast on 1 mil thick polyester film using a #52wire rod. The films were dried/cured for 5 days at ambient temperaturebefore testing. Formulations 1-4 contained no tackifying resin.Formulations 5-8 are the same as 1-4 except they also contain tackifyingresin, REGALREZ® 1085, at the same concentration as diol/monol.

Standard tests for rolling ball tack, Polyken probe tack, 180° peel andholding power were run on the adhesives after ambient temperature cure.This is the condition the adhesives would be in when they are being usedas pressure sensitive adhesives. Test specimens for 180° peel, holdingpower and Shear Adhesion Failure Temperature (SAFT) were prepared andbaked 1 hour at 100° C. This is the condition the adhesives would be inwhen they should be performing as structural adhesives. SAFT was notmeasured on the ambient cured adhesives because they would probably cureas the temperature in the test was increased.

The SAFT was measured by 1"×1" Mylar to Mylar lap joint with a 1 kgweight. SAFT measures the temperature at which the lap shear assemblyfails under load. Rolling Ball Tack (RBT) is the distance a steel ballrolls on the adhesive film with a standard initial velocity (PressureSensitive Tape Council Test No. 6). Small numbers indicate aggressivetack. Holding Power (HP) is the time required to pull a standard area(1/2 in.×1/2 in.) of tape from a standard test surface (steel, Kraftpaper) under a standard load (2 kg), in shear at 2° antipeel (PressureSensitive Tape Council Method No. 7). Long times indicate high adhesivestrength. 180° peel was determined by Pressure Sensitive Tape CouncilMethod No. 1. Large numbers indicate high strength when peeling a testtape from a steel substrate. Polyken probe tack (PPT) was determined byASTM D-2979. High numbers for PPT indicate aggressive tack.

After the adhesives had dried and cured for 5 days at ambienttemperature, the hydroxyl/isocyanate reaction was essentially complete.All of the films were coherent and, when touched, no adhesive wastransferred to the finger. The films were qualitatively rated forclarity and finger tack. Adhesives 2 and 6 stood out as unique. Theywere more hazy than the others, showing Polymer C has poor compatibilitywith Polymer A, and had poor finger tack, probably reflecting the impactof the styrene content in Polymer C. All the other adhesives were fairlyclear and generally had good finger tack.

Adhesives 1 and 5 are the control adhesives, without and with tackifyingresin, in which the monol (Polymer B) used has only the single hydroxylgroup and is not heterotelechelic. After ambient cure, these adhesiveshave good tack and they fail cohesively in the peel and holding powertests. After baking, holding powers improve, the peel strength ofadhesive 5 increases and the failure mechanism in the peel test onadhesive 1 switches from cohesive to adhesive failure. However, theholding power and SAFT of these two formulations after baking are muchlower than those of the other formulations.

Adhesives 2 and 6 have poor tack and high holding power after ambientcure. Peel and holding power do not change upon baking. The high peel,high holding power and high SAFT of adhesive 6 are impressive. Thissuggests that if higher than normal bonding pressure can be applied tomake the assembly to offset the poor tack after ambient cure, adhesive 6may perform quite well as a structural adhesive when baked.

Adhesives 3 and 7 used Polymer D. This monol contains no styrene so itshould maintain low glass transition temperature (Tg) and good tack inthe ambient cured adhesive. It not only has the hydroxyl group toparticipate in the ambient cure urethane reaction but also has epoxygroups to participate in the melamine reaction upon baking. Results inthe table show that, after ambient cure, adhesive 3 has only fair tackbut excellent holding power. After baking, adhesive 3 continues to haveexcellent holding power and has excellent SAFT. The failure mechanism inthe peel test is adhesive failure, suggesting that adhesive 3 hassubstantial cohesive strength after ambient cure and that its cohesivestrength increases upon baking since its peel value drops. The presenceof tackifying resin in adhesive 7 improves the Polyken probe tack andfinger tack in the ambient cured adhesive. The bake cured adhesive hasexcellent holding power and SAFT. The change in failure mechanism in thepeel test from a partial cohesive failure in the ambient cured adhesiveto a purely adhesive failure in the bake cured adhesive suggests thatthe cohesive strength of the adhesive increased as desired upon baking.

Adhesives 4 and 8 performed well, probably because the C═C unsaturationparticipated in the melamine curing reaction. Indeed, results in thetable show that adhesive 4 after ambient cure has good tack but lowholding power and fails cohesively in the peel test. However, afterbaking, it has excellent holding power and SAFT and the failuremechanism becomes adhesive in the peel test. These results suggest aclear increase in cohesive strength upon baking. Adhesive 8 containingtackifying resin has even better Polyken probe tack than adhesive 4. Ittoo shows an increase in holding power and peel strength upon baking,again suggesting an increase in cohesive strength.

                                      TABLE 1                                     __________________________________________________________________________                1   2    3    4    5   6    7    8                                __________________________________________________________________________    Composition, pbw                                                              Polymer A   1225                                                                              1225 1225 1225 1225                                                                              1225 1225 1225                             Polymer B   2275               2275                                           Polymer C       2275               2275                                       Polymer D            2275               2275                                  Polymer E                 2275               2275                             Desmodur ® Z-4370                                                                     663 524  524  524  663 524  524  524                              REGALREZ ® 1085            3500                                                                              3500 3500 3500                             DABCO T-12  2.08                                                                              2.01 2.01 2.01 2.08                                                                              2.01 2.01 2.01                             CYMEL ® 1156                                                                          768 768  768  768  768 768  768  768                              CYCAT ® 600                                                                           71  71   71   71   71  71   71   71                               Xylene      2444                                                                              2421 2421 2421 4777                                                                              4754 4754 4754                             Composition, % w                                                              Polymer A   25.9                                                                              26.4 26.4 26.4 14.9                                                                              15.1 15.1 15.1                             Monol (B,C,D or E)                                                                        48.1                                                                              49.1 49.1 49.1 27.6                                                                              28.0 28.0 28.0                             Z-4370 solids                                                                             9.8 7.9  7.9  7.9  5.6 4.5  4.5  4.5                              REGALREZ ® 1085                                                                       0.0 0.0  0.0  0.0  42.5                                                                              43.0 43.0 43.0                             CYMEL ® 1156                                                                          16.2                                                                              16.6 16.6 16.6 9.3 9.4  9.4  9.4                              Qualitative rating of films                                                   after 5 days ambient cure                                                     Clarity     Slight                                                                            Very Clear                                                                              Slight                                                                             Clear                                                                             Slight                                                                             Clear                                                                              Clear                                        Haze                                                                              Hazy      Haze     Haze                                       Finger Tack Good                                                                              None Fair Good Good                                                                              None Good Good                             Properties after ambient                                                      cure                                                                          Thickness, mil                                                                            2.1 1.9  2.0  2.0  2.3 1.9  2.0  2.0                              Rolling Ball Tack, cm                                                                     4   23   13   13   4   >28  18   15                               Polyken Probe Tack, kg                                                                    0.52                                                                              0.26 0.32 0.63 1.30                                                                              0.15 0.67 1.00                             180° Peel to CRS, pli                                                              1.3c                                                                              1.1a 1.4a 1.4c 3.0c                                                                              6a/c 7a/c 3.1c                             Holding Power, 1 × 1, 2 Kg                                                          74c >4000                                                                              >4000                                                                              23c  13c >4000                                                                              >4000                                                                              32c                              to CRS (D36), min                                                             Properties after bake cure*                                                   180° Peel to CRS, pli                                                              0.8a                                                                              0.9a 0.5a 1.2a 4.5c                                                                              4.8a 1.4a 4.5c                             Holding Power, 1 × 1, 2 Kg                                                          2500                                                                              >4000                                                                              >4000                                                                              >4000                                                                              1100                                                                              >4000                                                                              >4000                                                                              >4000                            to CRS (D36), min                                                             SAFT to Mylar, °C.                                                                 95  >168 >168 >168 75  >168 >168 144                              __________________________________________________________________________     a adhesive failure                                                            c cohesive failure                                                       

We claim:
 1. A pressure sensitive structural adhesive or sealantcomposition comprising:(a) a polymer system comprising from 95 to 15percent by weight of a hydroxy functional telechelic polymer and from 5to 85 percent by weight of a heterotelechelic polydiene block polymerhaving at least one hydroxyl group and another functional group selectedfrom the group consisting of C═C unsaturation and epoxidized olefin, and(b) a dual curing system wherein one element of the curing system curesthe telechelic polymer at ambient conditions such that a pressuresensitive adhesive or sealant is formed and the other element cures theheterotelechelic polymer upon sulfur or melamine cure and baking at atemperature of at least 100° C. To form a structural adhesive or sealantcomposition.
 2. The composition of claim 1 wherein the polymer systemcomprises a telechelic polymer containing hydroxyl functionality and aheterotelechelic polymer containing hydroxyl functionality and anotherfunctionality which is C═C unsaturation.
 3. The composition of claim 2wherein the dual curing system is comprised of an polyisocyanate havinga equivalent weight between 50 and 500 which is the curing agent for thetelechelic polymer and melamine which is the curing agent for theheterotelechelic polymer.